Grippers are traditionally used in conjunction with drilling in the ground or seabed for assembling and disassembling drill strings and borehole casings. The drill strings and the casings are made up of pipes, and two grippers can be used to grip a respective pipe to connect or disconnect the pipes at complementary threads in the pipes.
The dies, or inserts as they are also sometimes referred to, are the parts that are in direct contact with the pipes. They can have a surface presenting a curvature that is identical to the curvature of the pipe to be gripped. The dies often need to be replaced, due for example to a change of pipe diameter, or to wear of the dies. When such die changing is carried out during a drilling or a borehole preparation process, there a risk that loose parts, such as bolts falls into the borehole, which can cause severe problems.
US2003118400 suggests, where each die is inserted in a dovetail slot, providing a locking bracket in a further dovetail slot arranged perpendicularly to the dovetail slot for the die. The locking bracket can be displaced from a position wherein the die is locked by the locking bracket to a position where the die can be moved passed the locking bracket. For this a screw needs to be tightened, to keep the locking bracket in the locking position, and released when the die is to be replaced. However, there is nevertheless a risk that an operator makes a mistake when handling the locking device. More generally, there is a desire to further reduce the risks of errors and mistakes when the dies are replaced. This includes the risk that the operator makes a mistake when inserting replacement dies, which can damage the equipment.